Clothes drying machines, referred to as clothes dryers, dry damp clothing by circulating heated air among the clothing. Often, clothes dryers include a drum in which a load of damp clothing is placed. During a drying cycle, an electric motor rotates the drum and a blower circulates heated air among the clothing as the clothing tumbles within the drum. The drying cycle may continue until the expiration of a predetermined time period or until a control system determines that the clothing is substantially dry.
The electric motor coupled to the drum includes an output shaft having a fixed angular velocity or rotational speed. The rotation of the output shaft is typically coupled at one end to the drum, through a transmission system, to cause the drum to have an angular velocity suitable for most clothes drying situations, and at another end to an air blower that forces an air flow through the drum. In particular, if the drum is rotated too quickly the clothes within the drum may become forced against the sides of the drum instead of tumbling within the drum. Additionally, if the drum is rotated too slowly the clothes within the drum may remain grouped together, and prevent the heated air from flowing among the clothing sufficiently to dry the clothing. Therefore, the electric motor is chosen with reference to its angular velocity to produce an angular velocity for the drum at which an average load of damp clothing is dried within a reasonable time. The angular velocity of the motor output shaft, however, may not drive the air blower at an angular velocity, which produces a preferred amount of air flow, as explained below.
The air blower, or blower, often includes a fan mounted within a housing. When the fan is rotated within the housing, air is drawn into a housing inlet and expelled through a housing outlet. The air expelled from the housing outlet creates a vacuum in an outlet port of the drum for pulling air through the dryer for contacting the damp clothing tumbling in the drum. Depending on the drying cycle, a heating element, or heater, may be activated to heat the air before the air is drawn into the drum. The dry heated or unheated air circulates among the damp clothing causing water within the damp clothing to evaporate. As additional dry air is drawn into the drum, moisture laden air is extracted from the drum through an exhaust port of the drum via the blower. As would be readily understood by one skilled in the art, the blower may be adapted to blow air into the drum opposite as described above.
As noted above, the angular velocity of the motor output shaft is typically dictated by the number of motor poles and the electricity source frequency. With this relatively fixed value, a transmission system (e.g., a pulley) is used to produce a drum angular velocity suitable to tumble an average load of clothing. For instance, the dryer may have a two (2) pole line frequency electric motor coupled to a sixty (60) hertz (“Hz”) power supply in North America. This motor is configured to have an unloaded output shaft angular velocity of approximately 3,600 rotations per minute (“rpm”). Even with a transmission system, however, size constraints prevent this motor from reliably rotating a drum. Specifically, because the output shaft angular velocity must be reduced in order to rotate the drum at a preferred angular velocity, a transmission member having a very small diameter must be coupled to the output shaft and a comparatively larger transmission member must be coupled to drum. A power transmission device, such as an endless belt, is used to couple the rotation of the small diameter transmission member on the output shaft to the larger transmission member coupled to the drum. In order to achieve a preferred drum angular velocity; however, the transmission member coupled to the output shaft may be too small to engage reliably the endless belt. Furthermore, when the blower is driven at 3,600 rpm it may operate at a noise level that some users find objectionable.
To address this problem, clothes dryers may include a four (4) pole line frequency electric motor coupled to a sixty (60) Hz power supply. This motor is configured to have an unloaded output shaft angular velocity of approximately 1,800 rpm. An angular velocity of 1,800 rpm may be faster than a preferred angular velocity of the drum; however, the reduced angular velocity of the output shaft (as compared to a two (2) pole line frequency electric motor) enables a preferred drum angular velocity to be attained with a larger output shaft transmission member, which engages an endless belt or other power transmission device more reliably. An angular velocity of 1800 rpm, however, may be too slow to drive the blower at a speed that produces a preferred amount of air flow. Therefore, a second transmission is required to convert the angular velocity of the output shaft to a preferred angular velocity for driving the blower. In summary, a four (4) pole line frequency electric motor may function to rotate both a drum and a blower of a clothes dryer; however, two transmissions are required to convert the angular velocity of the output shaft to preferred angular velocities for driving the blower and rotating the drum. Therefore, further developments in the area of clothes dryers having a single electric motor, are highly desirable.